## Quantum Theory of Light

 7.1 Quantum Theory of Light

Electromagnetic spectrum

• All objects emits electromagnetic radiation.
• Cold objects $$\rightarrow$$ waves with low frequency (Eg: radio waves, microwave)
• Hot objects $$\rightarrow$$ waves with higher frequency (Eg: visible light and ultraviolet radiation)

 Black body An idealised body that is able to absorb all electromagnetic radiation that falls on it.

Classical Theory

1. The particle nature of light (Isaac Newton)
• Unsuccessful in explaining the phenomenon of light refraction due to failure in comparing the speed of light in glass and air

2. Double-slit experiment (Thomas Young)
• Unable to explain the radiation spectrum produced by black bodies

3. Dalton atomic model
• Unable to explain the light spectrum produced by atoms

4. Discovery of electrons
• Unable to explain the line spectrum of light produced by atoms

Quantum theory

1. Max Planck
• Introduced the concept of quantum (discrete energy) in 1900

2. Albert Einstein
• Einstein's quantum theory of light was susccessful in  explaining the characteristics of the photoelectric effect that could not be explained by classical theory

3. Niels Bohr
• Explained the production of line spectrum by hydrogen atoms

4. Louis De Broglie
• Introduced the hypothesis on the wave nature of particles in 1924

Electromagnetic spectrum may be a:

1. Continuous spectrum
2. Line spectrum

 Continuous spectrum The dispersion of white light by a prism consisting of seven visible colours.

 Line spectrum Produced by an excited atom is a series of colored lines with unique wavelengths and frequencies.

 Photon energy, $$E$$ $$E=hf$$, where $$h$$ = Planck constant ($$6.63\times10^{-34} \text{ J s}$$ $$f$$ = frequency of light waves

 Wavelength, $$\lambda$$ $$\lambda = \dfrac{h}{mv}$$, where $$m$$ = mass of particle, $$v$$ = velocity of particle

## Quantum Theory of Light

 7.1 Quantum Theory of Light

Electromagnetic spectrum

• All objects emits electromagnetic radiation.
• Cold objects $$\rightarrow$$ waves with low frequency (Eg: radio waves, microwave)
• Hot objects $$\rightarrow$$ waves with higher frequency (Eg: visible light and ultraviolet radiation)

 Black body An idealised body that is able to absorb all electromagnetic radiation that falls on it.

Classical Theory

1. The particle nature of light (Isaac Newton)
• Unsuccessful in explaining the phenomenon of light refraction due to failure in comparing the speed of light in glass and air

2. Double-slit experiment (Thomas Young)
• Unable to explain the radiation spectrum produced by black bodies

3. Dalton atomic model
• Unable to explain the light spectrum produced by atoms

4. Discovery of electrons
• Unable to explain the line spectrum of light produced by atoms

Quantum theory

1. Max Planck
• Introduced the concept of quantum (discrete energy) in 1900

2. Albert Einstein
• Einstein's quantum theory of light was susccessful in  explaining the characteristics of the photoelectric effect that could not be explained by classical theory

3. Niels Bohr
• Explained the production of line spectrum by hydrogen atoms

4. Louis De Broglie
• Introduced the hypothesis on the wave nature of particles in 1924

Electromagnetic spectrum may be a:

1. Continuous spectrum
2. Line spectrum

 Continuous spectrum The dispersion of white light by a prism consisting of seven visible colours.

 Line spectrum Produced by an excited atom is a series of colored lines with unique wavelengths and frequencies.

 Photon energy, $$E$$ $$E=hf$$, where $$h$$ = Planck constant ($$6.63\times10^{-34} \text{ J s}$$ $$f$$ = frequency of light waves

 Wavelength, $$\lambda$$ $$\lambda = \dfrac{h}{mv}$$, where $$m$$ = mass of particle, $$v$$ = velocity of particle